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Thread: M30B32 L-jet porting

  1. #1
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    '78 633CSi, '81 635CSi

    M30B32 L-jet porting

    Got one of these that hasnt ran in 20 years so rebuild is needed.

    What gains would i get (if any) with head porting?
    Would the enonomy improve?
    Could it be improved with lightening of the flywheel/crank/pistons?

    Car would be used as a 2nd one for trips and such, i would want to get the best out of the engine without turbocharging or any outside mods apart from the distributor and such.

  2. #2
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    1985 535i, 1980 635CSi
    The B32 has a good cam and runs pretty good in Motronic form but I don't know if the Ljet version has that cam. The head is basically the same as M30B34 US and other M30 engines except Ljet uses a different cam distributor end for the mechanical distributor.

    Otherwise the M30B35 has larger and smoother intake ports in the head as well as larger exhaust ports on the exhaust manifold. The M30b35 also has larger intake valves if you'd like to install those for a bit extra flow. There aren't a lot of gains to be had unless you go FI.

    Of course a 3+ angle valve grind and some porting will help-- anything to get more flow. But in general BMW maxed out these engines pretty good from the factory. Economy likely won't improve much.

    To really hop up the car you could bore out the block and make it to M90 specifications-- that engine is rev happy and outputs 218hp at 9.3:1 compression. It was offered in Ljet and runs good. At that point though you may as well change the crank and bring it up to 3.6L as well. The M90 cam is also slightly better than M30b35 but more difficult to find.

    I'd do a simple head refresh if possible using an M90 cam. Maybe upsizing intake valves to the 1mm larger valves, but making sure to do a 3 angle valve grind. Install some headers if you want a bit of extra power. Porting may work but you have to match the head to the intake manifold adapters for smooth transitions. Usually this costs $$ and 3 angle valve grind is better bang for your buck.

  3. #3
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    Thanks for the answer!

    There is an old man here that does the porting and matching for the head and both manifolds. The cost is about 200e/less than 250$ so that will be on the list.
    If i get a hold of an M90 engine i will make some mods on the B32 using its parts.

  4. #4
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    Quote Originally Posted by LeonardoL View Post
    Thanks for the answer!

    There is an old man here that does the porting and matching for the head and both manifolds. The cost is about 200e/less than 250$ so that will be on the list.
    If i get a hold of an M90 engine i will make some mods on the B32 using its parts.
    If you can get an M90, it would make sense to use it as the basis of a rebuild/porting and swap in place of your current engine

  5. #5
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    325is, 96 M3 Euro
    forget about spending money on port matching, refresh something on the engine that needs it before you do that

  6. #6
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    There is an 1980 M90 engine for sale in germany, i could probably get it for less than 500 euros (L-jet). So the camshaft between the B32 and M90 is just plug & play? Is it possible to bore out the B32 block to M90 spec and swapping the internals?

    I know the engine swap is the best and most budget friendly option however the M90 says 3.5 on the block. I would prefer it says 3.2 on the block (historic licence and no crap with the papers for swapped engine etc.) .
    However on the other hand i would still need to refresh the swapped engine because i wouldnt be too keen on driving an unchecked and no history engine on lond trips.

  7. #7
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    The patient, day 0.
    This is the one getting reworked.

    20180127_162612.jpg

  8. #8
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    Basicly, everything on the engine is great. No wear, even looks like it was rebuilt. Even the brake pads were almost new (rusted though, sitting since 1991). Makes me wonder what happened, maybe the owner passed, who knows...

    Now. Are the current L-jet injectors compatible with Megasquirt?

    I know i need to put in an crank sensor, and an O2 sensor, new throttle position sensor; seems that the water temp is compatible.

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